1. Technical Field
This disclosure relates to semiconductor fabrication, and more particularly, to a method for forming and filling trenches of different sizes in a single process.
2. Description of the Related Art
Shallow trench isolations (STI) structures are provided in semiconductor chips to isolate integrated semiconductor devices, such as, transistors. STI structures are formed in trenches etched from a silicon substrate or other materials adjacent to an active area of a semiconductor chip layout. These trenches are typically etched down to a depth of about 250 nm to 300 nm. These trenches are usually lined with a nitride liner and/or a thermally grown oxide liner and filled with an oxide material to provide isolation between semiconductor devices.
In certain situations, STI regions are required at greater depths. In these cases, aggressive filling of the trenches may cause voids or an incomplete fill. This can have consequences on chip yield and on device reliability. Therefore, very restrictive gapfill requirements are needed in order to ensure a complete fill. Further, since all trenches may not be of a same depth or same opening width, different processes may be needed to fill the different trenches.
Therefore, a need exists for a method of defining a depth for trench isolation structures which maintains an aspect ratio of the trenches to permit a complete fill.